This invention relates to refractory shapes and, more particularly, it concerns an improved design to join and align refractory tubular shapes such as used in the bottom pouring of steel.
As generally used in the steel making arts and as employed in this specification, the term, "bottom pouring" connotes the conveying of molten steel into a mold from or through its bottom. Typically, bottom pouring is done to improve surface quality of certain grades of steel, although bottom pouring is also practiced in those steel making facilities where continuous casting is not economical. Usually, bottom pouring is done to simultaneously fill with molten metal a gang of molds which are connected in series or parallel to a runner system composed of tubular refractory shapes.
The refractory tubular shapes used in a conventional bottom pouring process include a variety of configurations such as, tee outlets, ell outlets, and risers which are arranged in selected sequences to form continuous conduits. For example, the shapes are arranged in simple runner configurations or in complex configurations in which the runners are connected to a central distributor (spider) which directs the flow of metal to ingot molds placed in various localities. Such tubular refractory shapes are typically made from fireclay or high alumina compositions. The tubular shapes are pieced together in sections to form the "plumbing" or "pipe" required to transport molten melt from a ladle to a mold. The tubular shapes must be joined tightly to prevent leakage while the molten steel is being transported through the refractory "pipe".
Current bottom pouring techniques employ a simple male-to-female fit to piece the refractory tubular shapes together. Usually, a circular male projection at the end of one section fits into a corresponding circular female recess at the end of another section thereby forming a continuous conduit for the transport of the molten steel. Because the tubular refractory shapes are usually made from a relatively high proportion of crude clay, considerable shrinkage occurs during manufacture of the refractory section. Therefore, it is very difficult to maintain tight tolerances between the male projection and the corresponding female recess which join adjacent shapes. Typically, gaps of 1/8 inch are common.
To prevent metal leakage through the gap between the interfitting projection and recess of abutting refractory shapes, a refractory mortar is used to fill the gap. The gap allows for misalignment of the central bores of the shapes when the tubular sections are pieced together. If the bores are misaligned, the molten metal impacts a portion of an end face of at least one of the joined sections, and tends to push the refractory sections apart. The mortar-filled gap is also a source of weakness which is vulnerable to breakage due to mechanical stress and infiltration of molten metal. Further, a poor fit between refractory sections used to convey molten metal has lead in many instances to poor mold fill due to metal leakage before the mold. Moreover, a poor fit between a riser and an outlet can cause the riser to dislodge off of the outlet and float up in the molten steel within the mold. When this occurs, the ingot is usually scrapped.
In light of the foregoing, there is a need for an improved junction between tubular refractory shapes of the type referred to.